And WOW air isn't alone. Low-cost rival Norwegian Air is also offering flights from the U.S. to Europe for under $200. (Video via Norwegian Air Shuttle ASA)

Those two airlines are building on the same low-cost flight model that Spirit, Allegiant and Frontier have used in the U.S., and that Ryanair and easyJet have used in Europe. But are cheap trans-Atlantic flights too good to be true?

Airlines offering those super cheap flights also tack on ancillary charges and fees for things like hefty carry-ons or a seat assignment. Although those fees can sometimes double the price of the original ticket, it can still be cheaper than what many other commercial airlines offer.

And those low-cost flights to Europe from smaller carriers might look even more attractive now that major U.S. carriers pushed prices up a few bucks. TravelPulse reports United, Delta, American, Southwest and JetBlue all increased fares by $3.

According to USA Today, industry experts believe there's room for more low-cost airlines to begin offering cheap flights to Europe, like WOW and Norwegian. In the meantime, both airlines plan to add more flights from the U.S. to Europe. And prices could go even lower.